Adapted from Alice Mendrich’s Bittersweet
Yields 16 brownies
10 tablespoons unsalted butter
Position a rack in the lower third of the oven and preheat the oven to 325°F. Line the bottom and sides of an 8×8-inch square baking pan with parchment paper or foil, leaving an overhang on two opposite sides.
Combine the butter, sugar, cocoa, and salt in a medium microwave safe bowl. Heat for 60 seconds, then 30 second intervals. Stir from time to time until the butter is melted and the mixture is smooth and quite hot to the touch. Remove the bowl from the microwave and set aside briefly until the mixture is only warm, not hot.
Stir in the vanilla with a wooden spoon. Add the eggs one at a time, stirring vigorously after each one. When the batter looks thick, shiny, and well blended, add the flour and stir until you cannot see it any longer, then beat vigorously for 40 strokes with the wooden spoon or a rubber spatula. Stir in the nuts, if using. Spread evenly in the lined pan.
Bake until a toothpick plunged into the center emerges slightly moist with batter, 20 to 25 minutes. Let cool completely on a rack.
Lift up the ends of the parchment or foil liner, and transfer the brownies to a cutting board. Cut into 16 squares.